Diffraction-limited optics for single-atom manipulation

Abstract

We present an optical system designed to capture and observe a single neutral atom in an optical dipole trap, created by focusing a laser beam using a large-numerical-aperture $(\mathrm{NA}=0.5)$ aspheric lens. We experimentally evaluate the performance of the optical system and show that it is diffraction limited over a broad spectral range $(\ensuremath{\sim}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ with a large transverse field $(\ifmmode\pm\else\textpm\fi{}25\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$. The optical tweezer created at the focal point of the lens is able to trap single atoms of $^{87}\mathrm{Rb}$ and to detect them individually with a large collection efficiency. We measure the oscillation frequency of the atom in the dipole trap and use this value as an independent determination of the waist of the optical tweezer. Finally, we produce with the same lens two dipole traps separated by $2.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ and show that the imaging system can resolve the two atoms.